The source and form of carbohydrate for apricot fruit development

Abstract

During the 1981-1982 fruit growing season the length and diameter increase of apricot fruit (Prunus armeniaca L.) were recorded. Corresponding to this the glucose, fructose, sucrose and sorbitol levels of the fruit, bark and wood tissues and the xylem sap were determined. A number of field performed radioactive tracer experiments applying ¹⁴C - sorbitol or ¹⁴C - sorbitol plus ³H - sucrose to a small branchlet supporting developing fruit were also analysed to determine the radioactive concentration of the four specified carbohydrates in the different plant tissues.

It was concluded that analysis of fruit growth was best represented by including those fruit which remained on the tree until harvest as the fruit which fell prematurely were noticably smaller, especially in the latter part of the season. No major changes in the levels of glucose, fructose, sucrose and sorbitol were detected in any of the plant tissues as the fruit progressed from Stage II to Stage III. Sorbitol was the dominant endogenous carbohydrate in the bark and wood tissue and the xylem sap. Sorbitol appeared to be both the major translocate and a major storage form within the stem tissues. It did not readily enter the developing fruit at any time during the season when exogenously supplied ¹⁴C - sorbitol was applied at a point below the fruit. When ³H – sucrose was applied to the stem below the fruit it entered the fruit to a greater extent than sorbitol and it was concluded that sucrose was the carbohydrate form loaded into the fruit.

Within the fruit sucrose was thought to be hydrolysed to glucose and fructose up until the 8 January (two weeks before optimum fruit ripeness) after which the reverse process appeared to occur as a dramatic increase in sucrose was associated with a decrease in the fructose and glucose levels. The fruit tissue was still importing sucrose at this time.